Those skilled in the art of high-speed document processing, such as the sorting of bank checks and like financial instruments, know that the art involves using of machines and systems to move and process documents at sustained rates of thousands of documents per minute. Such machines must perform multiple inter-related operations upon each document as the documents travel by. Such operations might include, but are not limited to, printing on a document by contact, dot-matrix, or ink-jet means, reading data previously encoded thereon, and recording an archival image of the document by photographic or electronic imaging processes.
Those skilled in the art will further understand that documents moving through such machines must be accurately positioned to be processed accurately. For example, if a document carries a previously encoded line of magnetic characters (known in the art as MICR characters) and the machine is equipped to read and decode such characters, then the machine must present the document to such reading system in correct alignment and position. Other machine systems have similar requirements for correct and reliable alignment and positioning of documents passing through.
Those skilled in the art will further understand that document-processing now mandates the use of continuous-feed machines, in which the documents are fed in a continuous stream at very high speed with only negligible gaps between them. The processing rates presently required by customers could not be achieved without using such machines. For example, the Unisys DP1800 is a high-speed document processing machine that will feed 1800 standard documents per minute at a nominal track speed of 300 inches per second (ips) (7.62 meters per second), with an inter-document interval of a mere one-hundredth of a second (10 milliseconds).
Those skilled in the art will understand that such brief inter-document intervals do not allow a document to be individually aligned and adjusted relative to any process station. Instead, the document must be kept properly aligned as it passes the stations at all times. Even in "slower" machines (e.g. the Unisys DP500, with a minimal track speed of 100 ips or (2.54 meters per second), the interval between documents is still too brief to permit alignment of the document at each individual station.
Those skilled in the art will also understand that such document speed and feed rates requires special transport means, such as high-speed special transport friction-drive rollers and belts that are serially arranged to drive the document from point to point. The documents typically are trapped between opposing sets of such rollers and belts, and are constrained from distortion by flanking walls provided by the document track. Various process stations are then mounted along the walls, so the walls must be constructed and adapted to permit the process stations to operate upon the passing documents. The need for such transport means and associated track walls is essentially independent of the speed of the document. , in machines of"moderate" speed, such as the Unisys DP30 or the Unisys Teller-Scanner with a minimal track speed of 15 ips or 0.38 meters per second) require such transport means and associated track walls as well as such high-speed machines such as the Unisys DP1800.
Machines here contemplated are designed along these lines, with one convenient construction characterized by a narrow vertical track channel, with walls whose height approaches the vertical height of the documents, typically on the order of 4 inches (100 millimeters). Such track walls may include apertures of various shapes and sizes to permit the driving means (rollers, belts and so on) to drivingly contact documents in the track. While the track is preferably straight for ease of construction and best document flow, it may also include turns and comers. One finds that good, consistent feeding and driving of documents is obtained if the channel has a very small lateral width relative to its height. Optimal track width will usually vary with document speed. As an example, the nominal track width of the DP1800 product, with a track speed of 300 ips, is 0.10 inches (2.5 millimeters). At lower speeds, narrower track widths may be employed, with consequent improvement in document handling and alignment. As speeds increase, the track width must be increased somewhat, since the increased kinetic energy of the document makes it more likely to jam if the track is too narrow. Those skilled in the art will readily understand the trade-off between optimal document alignment and consistent document feeding and transport.
Such a construction, however, tends to bring problems of operations and service which are difficult to anticipate. Even though document process rates are increasing, customers still require ever-better machine reliability. With higher potential document processing rates, the impact of an unscheduled stoppage, such as a jam in the track, becomes proportionally greater. Jams and other track disruptions are typically very destructive events, because the machine cannot be stopped quickly enough to avoid driving follow-on documents into the jam-site. The result is typically the destruction of documents, which are crushed, folded and torn. Also, the machine may be rendered unserviceable for extended periods while the track is cleared and the involved documents accounted for.
Thus, jams in a document transport must be prevented, and extensive engineering effort is expended to minimize their occurrence. However, as document feed-rates rise, and as the nature and quality of the documents to be processed becomes more and more varied, jams continue to happen. Thus, recovery from the occasional jam should be as swift and non-disruptive as possible so that it poses minimal risk of damage to the machinery.
Jams are generally caused by a "discrepant" document that is torn, folded, or otherwise mutilated, or caused by foreign objects such as staples and paper clips that are attached to or entrained with a document. No matter how vigilant a machine-operator may be in inspecting documents before they are fed, the sheer volumes handled ensure that occasionally a jam will occur. When a jam occurs, the operator must clear the jam, retrieve the documents, remove any debris from the track, and restart the machine as quickly as possible.
One approach to this problem is to hinge or otherwise modify one or other of the track walls to allow an operator to access the track and remove jammed documents or other obstructions. This technique offers varying degrees of success. In some cases, the operator has extensive, adequate access to a track and its contents, but in many other cases, access is limited or blocked by machine parts, such as a read element. Also, this technique may require that not only the track walls, but also the driving rollers and belts be made hinged or demountable in like manner. This hinged or demountable construction increases complexity, cost, and failure rate of these mechanisms. Further, some track elements cannot be so constructed, especially those track elements such as print heads, optical heads, magnetic read heads, that involve integral functions. Nevertheless, this approach may be suitable in certain applications.
However, there are cases where the above approach is difficult to employ, such as in and around a machine process station. These cases are becoming more numerous as customers ask that more processing be integrated into a machine. For such cases, one should develop alternative means for machine operators to clear jammed documents and debris from a document track.
Other approaches to this problem involved using manual "ad hoc tools" fashioned by operators themselves, along with methods readily accessible to the operator. Various hooks and other implements have been used to probe the closed sections of a jammed track in an effort to dislodge and extract documents and debris. Such devices as wire coat hangers, spring-hooks, buttonhooks, and knitting needles have all been used. However, such techniques often damage the track and other delicate process devices, such as read heads, print heads, or optical reading devices that are incorporated along the track. In their desire to clear the machine as quickly as possible to resume operations, operators have occasionally so damaged the machine with improvised implements to put it out of action for hours or even days.